This invention relates to an alarm time detecting device for an alarm clock, and more specifically relates to improvement of an alarm time detecting mechanism having a hole on either an hour gear wheel or an alarm gear wheel and a projection on the other gear wheel. The mechanism of this type has been disadvantageous in forming thin type alarm clocks requiring a width corresponding to the axial shift of either the hour gear wheel or the alarm gear wheel. Furthermore, when a gear wheel having the hand is involved in the mechanism, the appearance of the alarm clock is spoiled as the hand moves axially and also disadvantageous requiring space for the shift of the hand.
To solve such problem in the conventional mechanism of this type, an alarm time detecting mechanism has been formed between a second hour gear wheel and a second alarm gear wheel engaging with the hour gear wheel and the alarm gear wheel, each having the needle, respectively. However, even in this arrangement, either the second hour gear wheel or the second alarm gear wheel has to be shifted in the axial direction requiring that the thickness of the gear to be engaged with the shifting gear should be increased so that the thickness of the thin type alarm clock has to be disadvantageously increased for a thickness corresponding to the distance of shifting of the gear wheel.